I've been looking at the migration data on BirdCast ( https://dashboard.birdcast.info/), and the numbers are not encouraging for the Pacific Flyway. We are seeing about half the expected numbers this Spring, and the last 5 years have been low except for 2023 which was a good year. This holds true for states up and down the Pacific Coast. When I sample states east of the Rockies the numbers seem to approximate the historic averages. It's not clear how the averages were established, but the Pacific Flyway is apparently an outlier.
Comparing Spring and Fall migration numbers prompts my real question. Eastern states see much higher numbers in the Fall. This seems logical if breeding birds are returning with hatch year birds. But Pacific states have much lower numbers in the Fall. Santa Cruz County sees about 20M birds in an average Spring, but fewer than 4M birds in the Fall (last year about 2M). This pattern holds for all Pacific states. Do western birds generally spread out their Fall migration in time or space? BirdCast focus for Fall is August-November which seems right. Do Pacific migrants spread out to the east or over the ocean? Am I misreading the data? What am I missing?
